The present invention relates to a magnetically driven positive displacement pump and thrust bearing assembly and in particular to a magnetically driven positive displacement pump having a thrust bearing assembly located within the fluid chamber of the pump for controlling rotor clearances with the cover and bracket faces of the fluid chamber.
The optimum clearances between the rotor and the cover and bracket faces in a positive displacement pump must be closely maintained during operation of the pump as these clearances are critical to providing a consistent flow of fluid from the pump. Centrifugal pumps, as opposed to positive displacement pumps, do not require that clearances between the rotor and the cover and bracket faces of the pump fluid chamber be as closely maintained during operation in order to provide a consistent flow of fluid from a centrifugal pump. Magnetically driven positive displacement pumps are shown and described in U.S. Pat. No. 5,165,868, issued Nov. 24, 1992, and U.S. Pat. No. 5,263,829, issued Nov. 23, 1993, both of which are assigned to Tuthill Corporation of Chicago, Ill., the applicant herein.
During operation of a positive displacement gear pump the rotor may be pushed towards the cover of the pump by a thrust force created by hydraulic loading on the rotor. The hydraulic loading on the rotor and the resulting thrust force are inherent in the design and operation of a positive displacement gear pump. The magnitude of the thrust force pushing the rotor towards the cover increases as the diameter of the rotor increases and as the pressure of the pumped fluid increases. As the rotor is pushed towards the cover, the clearances between the rotor and the cover and bracket faces of the pump chamber are changed thereby changing the operating efficiency of the pump. The rotor may also be forced into contact with the cover resulting in damage to the pump. The use of a thrust bearing in a magnetically driven positive displacement pump is made additionally difficult due to the exposure of the thrust bearing to the pumped fluid which may contain particulates or which may have poor lubricating qualities resulting in premature wear to the bearing.